Gaseous discharge tube system



Aug. 11, 1942.

J. D. L5 VAN GASEOUS DISCHARGE TUBE SYSTEM Original Filed Oct. 12', 1933I ATTORNEY Patented Aug. 11, 1942 UNITED STATE GASEOUS DISCHARGE runsSYSTEM James D. Le Van, Belmont, Mass, assignor to Raytheon ProductionCorporation, Newton, Mass, a corporation of Delaware Application October12, 1933, Serial No. 693,294 Renewed September 6, 1938 11 Claims.

This invention relates to systems utilizing gaseou s discharge tubes ofthe type in which an ionizing gaseous discharge serves as a source ofcurrent carriers for a controlled space discharge.

One of the objects of the invention is to provide a simple and effectivemeans for controlling the mutual conductance of such a tube.

Another of the objects of this invention is to provide a particularlysimple and effective amplifying circuit for the discharge tube of thetype described above.

The objects and novel features of the invention will bebest understoodfrom the following description of exemplifications thereof, referencebeing had to the accompanying diagrammatic drawing, wherein:

Fig. 1 is a diagram illustrating one embodiment of my novel system andshowing a tube in section which may be used therein:

Fig. 2 is a diagram of another embodiment of my invention; and

Fig. 3 is a curve showing one of the characteristics of the tubeillustrated.

In Fig. 1 the gaseous discharge tube which I utilize consists of agas-filled envelope I, preferably of glass, having a reentrant stem 2,the upper 'end of which carries a press 3 in which are sealed a numberof lead-in electrode supporting wires. Above the press and within theenvelope I are supported a number of electrodes. these electrodesconsists of a cathode 4. This cathode is of the usual type of indirectlyheated cathode ordinarily used in vacuum tubes, and consists of a hollowmetal cylinder 5 coated on the exterior thereof with electron-emittingmaterial 6, such as, for example, the oxides of alkali earth metals. Thecoating is heated to thermionic emission by means of an internal heaterconsisting usually of a coil of fine wire. The two ends of the heatingfilament 1' and 8 are connected to the two' wires 9' and I0 sealed inthe press 3. Surrounding the cathode 4 is the socallo'd cathanode I.This cathanode consists of an ':extended electrode having perforationsover its .surface, and preferably is in the form of a fine wire grid.Surrounding the cathanode 'I and substantially concentric therewith isthe control element 8 which likewise consists of an electrode ofsubstantial area having perforations over its surface and which ispreferably in the form of a fine wire grid. Surrounding all of the otherelectrodes and substantially concentric therewith is the anode 9 whichis preferably formed of a thin solid metal plate. The cathanode ispreferably supported in position by means of supporting One of standardsII and I2. Two metal-plates l3 and I4 close the upper and lower openends of the cylindrical cathanode I. The plates I3 and I4 have anopening it in the center thereof through which the cathode 4 passesfreely. The cathode 4 is supported from the two plates l3 and I4 bymeans of insulators I6 and H. The control electrode 8 is supported bysupporting standards [8 and I9 while the anode 0 is supported from asupporting standard by havinga radial member 2| extending from saidanode 9 and engaging said supporting standard 20. All of said electrodesare maintained in a definite relative position by the two insulatingplates 22 and 23, which have small openings whichreceive the upperandlower ends respectively of the various supporting standards. Externalconnections to the heatporting standard 20 for the anode 9 also has itslower end sealed in the press 3, and an external conductor 30 connectedthereto establishes an external connection for said anode. An additionalsupporting standard 3| whose lower end is sealed in the press 3 passesthrough openings in the upper and lower insulating members 22 and 23,respectively, and serves. as an additional support for the electrodestructure. The

lower end of the supporting standard IQ of the control electrode 8 iswelded to the supporting standard 3|. An external conductor 32 connectedthereto establishes an external connection to the control element 8. Theenvelope I is evacuated in accordance with the usual vacuum technique.After the tube has been evacuated, it is filled with a gas filling, suchas helium The gas pressure of the fill.-

ever, this gas pressure is sufficiently high so that an ionizingdischarge can be maintained between the cathode 4 and the cathanode lwhichproduces suflicient positive ions to neutralize the space chargebetween said two electrodes. When a vapor is used, such as, for example,mercury vapor, a quantity of mercury 33 is introduced into the utbe.

The tube as described above operates substantially in accordance withthe principles as set forth in my co-pending application, Serial. No.477,495, filed August 25, 1930. By establishing a discharge between thecathode 4 and the cathanode I, the gas in the space between said twoelectrodes is ionized. A large number of the electrons which pass intothe gaseous discharge space between the cathode and the cathanode andflow toward the cathanode I will pass through the screen openings insaid cathanode, and once having gotten into the space outside of saidcathanode, will come under the influence of the control electrode 8. Thespacing between the anode 9 and the cathanode l is such that under thepressure conditions existing in the tube, the distance between theopposing electrode surfaces is of the order to magnitude ofthe mean freepath of the molecules in the gas. Due to this spacing, a comparativelylarge voltage can be impressed across these electrodes withoutintroducing independent ionizing discharges therebetween. With greaterspacing, such voltages would produce independent ionizing dischargeswhich are very difficult to control by such a control member as 8. Withthe shorter spacing, any dischar'ges'which occur between the anodes 8and the cathanode l are directly the result of electrons which pass fromthe gaseous discharge space through the openings in the cathanode I.Under these conditions a complete control of this discharge can besecured by a potential on is laid off along .the horizontal axis; Gmrepresents the mutual conductance of the tube, and is laid off along thevertical axis. As the values of mutual conductance are plotted againstthe values of cathanode current, we obtain the curve C as shown in Fig.3. From such a curve I have determined that the mutual conductance bearssubstantially the following relationship to the cathanode current:

. where K is a constant depending upon the pathe controlmember 8. Itwill be noticed that in the construction, as shown, there are variouselements, such as the supporting standards connected to the anode, thecathanode and the control grid, between which paths of substantiallygreater length than the spacing between these various electrodes exist.If free electrons in considerable number .were allowed to escape fromthe gaseous discharge space between the -cath ode and the cathanode intothese relatively long discharge spaces, independent and uncontrollablegaseous discharges might occur between the anode, the control electrode,and the cathanode. Such discharges would very likely destroy the controlfeatures of the control grid, and therefore it has been necessary toadopt some means for preventing such uncontrollable discharges fromoccurring. This has been done by preventing electrons or other currentcarriers generated in the discharge space between the cathanode and thecathode from escaping into said long discharge spaces. First of all, theupper and lower ends of the cathanode have been closed by the two platesl3 and I4, thereby preventing escape of electrons from the dischargespace through the ends of the cathanode. After the electrons have passedfrom the cathanode, the spacing between the cathanode, the control grid,and the anode is so small that there is substantially no tendency forthe electrons to escape mutual conductance of the tube and the cathanodecurrent of certain tubes of the present type which I have tested isshown in Fig. 3, in which Ica represents the amount of current flowingbetween the cathode and the cathanode, and

rameters of the tube. While this condition exists in certain tubes whichI have examined, it may be possible that the particular relationshipbetween these qualities may differ with different types of construction.However, in each gaseous discharge tube of the general type which I haveillustrated, there will be some such definite relationship between themutual conductance of the tube and the cathanode current as I haveindicated above.

In order to utilize the above feature of my invention, the tubeillustrated may be connected in some such circuit as illustrated inFig. 1. In this system the heating filament is furnished with heatingcurrent by connecting the wires 24 and 25 to some suitable source ofheating current, such as the battery 34, the amount of current beingdetermined by the resistance 35 in series with said battery. The signalto be I amplified is impressed upon the terminals 36 and 31 of theprimary 38 of a coupling transformer. The secondary 39 of said couplingtransformer may have connected across its terminals a variable tuningcondenser 40. One terminal of said secondary 39 is connected through theconductor 32 to the control electrode 8. The other end of said secondary39 is connected through the biasing battery 4| to cathode conductor 28.In this manner the signal impressed across the terminals 36 and 31 is inturn impressed between the cathode 4 and the control electrode 8, thebiasing battery 4| giving to the control electrode 8 a negative bias.This bias may be of any convenient value. In typical embodiments of myinvention I have used values of negative bias ranging from 0 to 5 volts.The potential for the maintaining of the ionizing discharge between thecathode 4 and the cathanode l is supplied by a battery 42, thepositivepole of which is connected to the cathanode 1 through theconductor 29, and the negative pole of which is connected through acontrolling device 43 to the conductor 28 leading to the oathode 4. Thecondition which the value of the potential supplied by the battery 42must satisfy is that it must be sufiicient to impress between thecathode 4 and the cathanode l a potential sufficient in magnitude tosustain an ionizing discharge between said electrodes. In order toprevent the anode current from producing undesirable changes incathanode current, I prefer to utilize a high value of potential for thebattery 42 and connect in series therewith a device across which thepassage of the current from the battery 412 will produce a comparativelyhigh drop, preferably several times the potential appearing between thecathode 4 and the cathanode 7. If a high vacuum tube is utilized as thecontrol device 43, such a tube will have a sufficiently high drop acrossit to take care of this effect. If, however, some other type of controldevice having an inherently low voltage drop is used, it may benecessary to connect an additional resistance in series therewith toproduce the necessary total voltage drop external to thecathode-cathanode discharge path. In typical embodiments of my inventionI have utilized values of potential of the battery 2 ranging from about50 volts to 150 volts. A battery 44 has its negative pole connected tothe cathode & through the cathode conductor 28, and has its positivepole connected to one end of the primary 45 of an output couplingtransformer. The other end of said primary 45 is connected to theconductor 39 which in turn is connected to the anode 9. The voltage ofthis battery 44 should be sufiiciently high to impress between thecathode 4 and the anode 9 a potential substantially higher than thatappearing between the cathode 4 and the cathanode T. The voltage betweenthe cathode 4 and anode 9 in typical embodiments may be between 50 and500 volts. Of course higher or lower voltages may be used with difierenttypes of tubes. The secondary 46 of the output coupling transformer mayhave connected across its terminals a tuning condenser 41. Saidsecondary 46 and condenser 41 may constitute portions of a detectorstage it. This detector stage may take any conventional form whichpossesses as one of its features an automatic volume control outputvoltage. A great number of detector stages of this type are known in theart, and it is believed to be unnecessary to illustrate any particularform of said detector stage 48. The automatic volume control voltage maybe taken off from the detector stage from the two terminals 59 and 50 towhich are connected the conductors and 52, respectively. As is wellknown, in an automatic volume control device, the voltage appearingacross this portion of the detector stage is one which varies inmagnitude in accordance with the magnitude of the signal voltageimpressed upon the detector stage. In the particular embodiment which Ihave shown, the control device 43 may take the form of a space dischargetube having a cathode 53 and an anode 54, between which the discharge iscontrolled by a control grid 55. The detector stage as is arranged insuch a way that the terminal dd becomes increasingly negative with anincrease in the magnitude of the signal voltage impressed upon thedetector stage. The terminal as which is positive with respect to theterminal as is connected through the conductor 52 to the positiveterminal of the battery d2 while the terminal as is connected throughthe conductor St to the control grid 55.

Upon connecting the device as shown and impressing a signal voltageacross the terminals 38 and 3?, the signal will be amplifia by thegaseous amplifier tube, and the amplified output thereof will beimpressed upon the detector stage $8. With a very weak signal, thenegative potential upon the control grid 55 will be very low, thusallowing a comparatively large amount of current to flow through thecontrol device as,

. and between the cathode and the cathancde i.

From Fig. 3 we see that by allowing a compara tlvely large amount ofcurrent to how from the the amount of current flowing through said con--trol device. Therefore, upon such an increase in impressed signal, thecurrent flowing between the cathode and the cathanode will decrease.Such a decrease in cathanode current will produce a decrease in themutual conductanc of the tube in accordance with the characteristic asshown in Fig. 3. Therefore, an increased signal impressed upon thedevice will be amplified by the gaseous amplifier tube to a lesserdegree than a weaker signal. The various constants of the system can beso selected that the resultant effect is to produce a substantiallyconstant out-- put from the detector stage 48 with a varying intensityof signal input at the terminals 36 and 31. Thus the arrangement asshown produces a particularly simple and effective automatic volumecontrol for the system disclosed.

Although in 1 I have illustrated variation in the mutual conductance ofmy gaseous amplifie'r tube by automatic means responsive to theintensity of a signal impressed upon the amplifier, yet there are agreat number of other systems in which it may be desired to have themutual conductance of the gaseous discharge tube vary in accordance withsome other quantity. Thus in Fig. 2 I have illustrated an amplifiersystemutilizing my gaseous discharge tube, in which I have indicateddiagrammatically means to independently vary the current between thecathode and the cathanode in order to vary the mutual conductance of theamplifier tube. In Fig. 2 the same reference numerals are applied toelements corresponding to those disclosed in Fig. 1. However, instead ofcontrolling theamount of current between the cathode 4 and the cathanode1, due to the impressed voltage of the battery 42 by such a controllingdevice as shown in Fig. 1, I utilize any other convenient controllingdevice. such as an adjustable resistance 55 in series with the battery42 in the cathodecathanode circuit. manually adjustable. or any otherdesired means of varying this resistance may be utilized. Thus,

for example, if it is desired to control the dethe cathanode and thecontrol electrode, I have found that the device shown herein operates ina much more satisfactory manner if the signal to be amplified isimpressed directly between the cathode 4 and the control electrode 8, asshown in Figs. 1 and 2.. Due to the fact that the current between thecathode and the cathanode flows through a circuit which issubstantiailyin dependent of the output flowing in th anode circuit. the amount ofanode current has substantially no effect upon the cathode-cathanodecurrent. Thus with any setting of the system shown. either in Fig. l orFig. 2, in which a dellnite amount of cathanode current is permitted tohow between the cathode and the cathanode This resistance 56 may be IGUYS.

of the controlling device, the mutual conductance of the tube willremain substantially constant even with large variations in anodecurrent.

Of course it is to be understood that this invention is not "limited tothe particular details or construction as described above, as manyequivalents will suggest themselves to those skilled in the art. Forexample, instead of taking the automatic volume control voltage from adetector stage, this voltage may be taken from any other part of asystem in which a voltage varying in accordance with the magnitude ofthe signal oc- Further, although I have shown my system associated withthe particular kind of gaseous amplifier device, this system can beutilized of current carriers for a controlled discharge with any gaseousamplifier in which a gaseous V discharge is to be utilized as as'ourceof current carriers for a discharge space controlled by some controlelement. Various other changes in my system will readily suggestthemselves.

It is accordingly desired that the appended claims be given a broadinterpretation commensurate with the scope of the invention within theart. i

What is claimed is:

1. In a gaseous discharge tube system, a gaseous space discharge tubecomprising a gas-filled envelope containing means for producing agaseous discharge through a space within said envelope, said gaseousdischarge serving as a source of current carriers for a controlled .dis-

charge space, control means for controlling the discharge through saidcontrolled discharge space, and an output electrode to which thecontrolled space discharge passes, and means for automatically varyingthe amount of current in said gaseous discharge space for varying themutual conductance of said. tube in response to a predeterminedcontrolling factor.

2. In a gaseous discharge tube system, a gaseous space discharge tubecomprising a-gas-filled envelope containing means for producing agaseous discharge through a space within said envelope, said gaseousdischarge serving as a source of current carriers for a controlleddischarge space, control means for controlling the discharge throughsaid controlled discharge space, and an output electrode to which thecontrolled electrode can pass into a controlled discharge spacedischarge passes, means for impressing a signal on said control means,and means responsive to the magnitude of said signal for automaticallyvarying the amount or current in said gaseous discharge space forvarying the mutual conductance of said tube in accordance with themagnitude of said signal.

.3. In a gaseous discharge tube system, a gaseous space discharge tubecomprising a gas-filled envelope containing means for producing agaseous discharge through a space within said envelope, said gaseousdischarge serving as a source of current carriers for a controlled discharge space, control means for controlling the discharge through saidcontrolled discharge space, and an output electrode to which thecontrolled space discharge passes, a controlled space discharge tubeassociated with said means for producing said gaseous discharge forvarying the amount of current in said gaseous discharge space forvarying the mutual conductance of said tube. I

4. In a gaseous discharge tube system, a gaseous space discharge tubecomprising a gas-filled envelope containing means for producing agasespace, control means for controlling the discharge through saidcontrolled discharge space, and an output electrode to which thecontrolled space discharge passes, a controlled space discharge tubeassociated with said means for producing said gaseous discharge forautomatically varying the amount of current in said gaseous dischargespace for varying the mutual conductance of said tube in accordance witha predetermined controlling factor.

5. In a gaseous discharge tube system, a gaseous space discharge tubecomprising a gas-filled enevelope containing means for producing agaseous discharge through a space within said envelope, said gaseousdischarge serving as a source of current carriers for a controlleddischarge space, control means for controlling the discharge throughsaid controlled discharge space, and an output electrode to which thecontrolled space discharge passes, means for impressing a signal on saidcontrol means, a controlled space discharge tubeassociated with saidmeans for producing said gaseous discharge for varying the amount ofcurrent in said gaseous discharge space for varying the mutualconductance of said tube, said last-named tube being controlled by acontrol element, means ior varying said control element in accordancewith the magnitude of said signal, whereby said last-named tubeautomatically varies the mutual conductance or said tube in accordancewith the magnitude of said signal.

6. In a gaseous discharge tube system, a gaseous space discharge tubecomprising a gas-filled envelope containing a cathode and a cooperatingelectrode between-which a gaseous discharge is adapted to take place,said cooperating electrode having openings through which electrons fromthe space between said cathode and cooperating space, control means forcontrolling the discharge through said controlled discharge space, andan output electrode to which the controlled space discharge passes, andmeans for automatically varying the amount of current in said gaseousdischarge space for varying the mutual conouctance of said tube inresponse to a predetermined controlling factor.

7. In a gaseous discharge tube system, a gaseous space discharge tubecomprising a gas-filled envelope containing a cathode and a cooperatingelectrode between which a gaseous discharge is adapted to take place,said cooperating electrode having openings through which electrons fromthe space between said cathode and cooperating electrode can pass into acontrolled discharge space, control means for controlling the dischargethrough said controlled discharge space, and an output electrode towhich the controlled space discharge passes, said output electrode beingspaced from said cooperating electrode a distance sufficiently short toprevent independent ionizing discharges between said output electrodeand cooperating electrode under comparatively high potentials appliedtherebetween, means for preventing ions or electrons from the space inwhich said first-mentioned discharge takes place from passing intospaces through which comparatively long ionizing paths between saidoutput electrode and cooperating electrode exist, and means forautomatically varying the amount of current in said gaseous dischargespace for varying the mutual conductance of said tube in accordance witha predetermined controlling factor.

8. In a gaseous discharge tube system, a gastrode through saidcooperating electrode into a controlled discharge space, control meansfor controlling the discharge through said controlled discharge space,and an ouput electrode to which the controlled space discharge passes, acircuit for impressing a" positive potential on said output electrodewith respect to said cathode, a circuit substantially independent of andunaffected by current flowing in said first-named circuit for impressinga potential between said cathode and said cooperating electrode, meansin said second-named circuit for varying the amount of space currentflowing between said cathode and said cooperating electrode for varyingthe mutual conductance of said tube, and an output device connected tosaid output electrode.

9. In a gaseous discharge tube system, a gaseous space discharge tubecomprising a gasfilled envelope containing a cathode and a cooperatingelectrode between which a gaseous discharge is adapted to take place,said cooperating electrode being adapted to pass electrons from thespace between said cathode and cooperating electrode through saidcooperating electrode into a controlled discharge space, control meansfor controlling the discharge through said controlled discharge space,and an output electrode to which the controlled space discharge passes,a circuit for impressing a positive potential on said output electrodewith respect to said cathode, a circuit substantially independent ofsaid firstnamed circuit for impressing a potential between said cathodeand said cooperating electrode, a relatively high impedance in serieswith said cathode and cooperating electrode in said second-namedcircuit, and an output device connected to said output electrode.

10. In a gaseous space discharge tube comprising a gas-filled envelopecontaining means for producing a gaseous discharge through a spacewithin said envelope, said gaseous discharge serving as a source ofcurrent carriers for a controlled discharge space, control means forcontrolling the discharge through said controlled discharge space, andan output electrode to which the controlled space discharge passes, themethod of varying the mutual conductance of said tube which consists invarying the amount of current in said gaseous discharge space.

11. In a gaseous discharge tube system, a gaseous space, discharge tubecomprising a gasfilled envelope containing means for producing a gaseousdischarge through a space within said envelope, said gaseous dischargeserving as a source of current carriers for a controlled dischargespace, control means for controlling the discharge through saidcontrolled discharge.

